When the Universe Unleashes Mega-Cosmic Collisions

Beyond the image we have of it from our planet, the Universe is in reality the scene of events of rare violence. Collisions of galaxies, supernovas, asteroid and comet impacts... The Universe is subject to phenomena that keep it constantly evolving.

Thanks to some of these events, the Earth has been able to evolve until it became conducive to the appearance of life and mankind.

Exceptional scientific advances in the field of astronomy allow us to understand and even observe live this violence above our heads.  

Cosmic Collision

The collision between two galaxies is an ordinary phenomenon in the evolution of galaxies. It occurs when two galaxies collide at sufficient speed to merge. The gas and dust of the two galaxies will then interact. The interstellar medium is disturbed and heated. The shock can trigger a starburst, also known as a starburst galaxy, in one of the two galaxies. This phenomenon generates an exceptional rate of star formation in one of the galaxies. These bursts are temporary, because if the rate of star formation were to remain so high, the reservoirs of star-forming gas would be completely dissipated much faster than the dynamic lifetime of the galaxy. The stars present in the two galaxies, meanwhile, do not generally collide with each other, as the distances between stars .

A starburst is generally defined by three factors: the star formation rate, which is the rate at which the galaxy converts gas into stars; the amount of gas available to form stars; and the comparison between the star formation period and the age of the galaxy. For a starburst to occur, a large quantity of molecular gas must be concentrated in a small volume. This usually occurs during galaxy mergers. 

Categorizing the various starbursts is not straightforward, as not all galaxies share the same specific characteristics. Starbursts can occur in the galactic disk or be scattered throughout the galaxy. Nevertheless, astronomers are currently discussing a number of classes. 

The subtypes of starbursts currently defined are blue compact galaxies, infrared luminous galaxies and Wolf-Rayet galaxies.

Compact blue galaxies have low mass and low metallicity. Dust-free, they contain a large number of relatively young, hot stars. As a result, they are luminous in the blue and ultraviolet. Astronomers initially thought these galaxies were young, but old stellar populations have been found in a number of them. In addition, the majority of compact blue galaxies show evidence of recent interactions.

Infrared-luminous galaxies are characterized by extremely high dust concentrations. They emit a red color because the ultraviolet radiation they emit is absorbed by dust and re-emitted as infrared. Most of the infrared-luminous galaxies observed show a double-core system. This suggests that star formation may have been triggered by galaxy mergers. 

In Wolf-Rayet galaxies, the majority of bright stars are Wolf-Rayet stars.

00:00:00 - Introduction

00:01:55 - Colliding galaxies

00:06:28 - Antenna galaxies 

00:10:37 - ARP 220

00:11:56 - ARP 147

00:14:18 - Andromeda Galaxy 

00:16:07 - Supernovas 

00:19:02 - SN 1987A

00:22:41 - SN 1993J

00:23:18 - SN 1572

00:26:43 - SN 1604

00:30:30 - SN 1054

00:34:10 - SN 2014J 

00:36:28 - Quasars 

00:39:49 - 3C 273

00:40:47 - 3C 186

00:42:15 - Cosmic collisions play major role in history of Earth formation 

00:42:35 - Formation of the Moon

00:49:54 - The Great Bombardment

00:57:54 - Asteroid and comet impacts

01:01:38 - Impact on Earth: the Chicxulub crater

01:06:10 - Vredefort crater

01:08:08 - Sudbury crater

01:09:10 - Maniitsoq Crater

01:10:03 - Barringer crater 

01:12:18 - Warburton crater

01:13:27 - Popigaï crater

01:14:27 - Manicouagan crater

01:15:09 - Shoemaker-Levy comet 

01:01:38 - What's next?